During conventional oil and gas well drilling, a drill bit attached to one end of a drill string is rotated into and through a formation in order to drill the well. Drilling fluid, also known as “drilling mud”, is pumped through the drill string and into the well to provide lubrication, to flush away drill cuttings, and to counter the pressure of formation fluid. Examples of formation fluid comprise oil, gas, and water.
In some situations, however, the pressure of the drilling fluid against the annular surface of the well (“drilling fluid pressure”) substantially differs from the opposing pressure of the formation fluid (“formation fluid pressure”). If the drilling fluid pressure is too low relative to the formation fluid pressure, formation fluid may enter the well; this is referred to as an “influx event” or a “kick”. In certain situations, an influx event may lead to a blowout, which is potentially a devastating drilling event.
If the drilling fluid pressure is too high, it can overcome the fracture strength of the formation, which can result in loss of drilling fluid to the formation; this loss of drilling fluid is referred to as a “loss event”. A loss event can consequently reduce the drilling fluid pressure, which may result in an influx event.
Given that both influx and loss events may lead to a blowout, there exists continued research and development into methods, systems, and techniques for detecting influx and loss events.